1. Field of the Invention
The present invention relates to a piston assembly of a shock absorber, and more particularly, to a piston assembly of a shock absorber which can easily control a damping force in a low-speed and middle-speed transition period.
2. Description of the Related Art
Generally, a shock absorber is designed to support a weight of a vehicle body and suppress and dampen a vibration transferred from a road surface to the vehicle body, contributing to improving a ride comfort and protecting loaded goods and various parts of a vehicle.
Such a shock absorber includes a cylinder filled with a working fluid (oil), a reciprocating piston rod connected to a vehicle body, and a piston valve connected to a lower end of the piston rod to slide within the cylinder and control a flow of the working fluid.
Herein, the term “blow-off point” as used herein refers to a point at which a two-dimensional damping force characteristic in a low-speed driving period meets a one-dimensional damping force characteristic in a middle-speed driving period. At the blow-off point, a rapid variation occurs in the damping force. Hence, the blow-off point is one of factors that degrade a ride comfort and give a passenger an unpleasant feeling.
The blow-off may be reduced by generating one blow-off point at two positions. However, this method has limitations in generating soft and smooth damping force characteristics in a low-speed and middle-speed transition period.